1. Field or the Invention
The present invention relates to an improved elastic body apparatus. More particularly, it relates to an elastic body apparatus used, e.g., in the suspension system for an automobile, or a liquid pressure regulator for an anti-lock brake thereof, etc.
2. Description of the Prior Art
Liquid pressure control devices for anti-lock brakes are well known in the art. See, for example, U.S. Pat. No. 4,600,245 and Canadian Patent No. 1,256,966.
As the elastic body apparatus used for a suspension system or the like for automobiles, various devices have been heretofore known which use a spring force of compressed air sealed by a flexible member. However, the prior art as noted above has problems. For example, in the case where a set load of the spring force is increased, if the effective pressure receiving area is increased, miniaturization thereof cannot be attained. In addition, if a pressure-resisting strength of a flexible member is increased so that a high pressure of compressed air may be used, it becomes difficult to obtain a suitable flexibility.
FIG. 4 shows an elastic body apparatus which uses both a pneumatic spring and a coil spring in order to obtain a great spring force in a small-sized device, the apparatus being applied to a liquid pressure regulator or control device for an anti-lock brake.
A master cylinder 2 actuated by application of a brake pedal 1 is connected to an end brake 6 via a liquid pressure regulator 5 by brake tubes 3 and 4. The liquid pressure regulator 5 houses a movable liquid pressure regulating piston 7 and a pressure differential responsive piston 8 formed integral therewith. The liquid pressure regulating piston 7 is slidably received within a small diameter cylinder 9 and the pressure differential responsive piston 8 is slidably received within a large diameter cylinder 10. Pistons 7 and 8 are provided with annular seals 11, 12 and 13, 14, respectively.
A lid member 15 is secured at the upper portion of the liquid pressure regulator 5, and a pneumatic pressure chamber 16 is formed between the lid member 15 and the pressure differential responsive piston 8. Gas having a predetermined pressure is sealed into the pneumatic pressure chamber 16, and a coil spring 17 is also inserted compressible with a predetermined mounting load. The pneumatic pressure chamber 16 and the coil spring 17 constitute an elastic body apparatus which downwardly urges the pressure differential responsive piston 8 (a movable member) and the liquid pressure regulating piston 7.
At the lower portion of the liquid pressure regulator 5 are provided an input hole or inlet 18, a valve chamber 19, a liquid pressure regulating chamber 20 and an output hole or outlet 21, the input hole 18 and the output hole 21 being connected to the brake tube 3 and the brake tube 4, respectively. An opening and closing valve 22 is mounted between the valve chamber 19 and the liquid pressure regulating chamber 20, the valve 22 being opened, in a normal state, by being pushed down by a pin 23 secured to the lower end of the liquid pressure regulating piston 7. A spring 24 serves to urge or bias valve 22 in a direction toward its "closed" position.
An annular liquid pressure chamber 25 is formed below the pressure differential responsive piston 8, the chamber 25 being connected to an electromagnetic valve means 27 by means of a liquid pressure tube 26. The electromagnetic valve means 27 is turned ON and OFF by an electronic control unit (not illustrated). An inlet side of the electromagnetic valve means 27 is connected to a discharge side of a pump 29 through a supply pipe 28, and a release side thereof is connected to a liquid tank 31 of the pump 29 through a conduit 30.
In the vehicle being operated, when the brake pedal is stepped on or depressed by the driver, the brake liquid pressure produced in the master cylinder 2 is supplied to the end brake 6 via the brake tube 3, the input hole 18, the valve chamber 19, the liquid pressure regulating chamber 20, the output hole 21 and the brake tube 4 to effect braking operation. However, when the aforesaid brake liquid pressure is excessively supplied with respect to a proper friction between the tires and the road surface and the wheels tend to lock, the electromagnetic valve means 27 is turned ON by the ON-signal of the electronic control unit (not shown), and the liquid pressure of the pump 29 is supplied to the liquid pressure chamber 25.
When the pressure differential responsive piston 8 is moved upward, due to the liquid pressure supplied to the liquid pressure chamber 25, against the pressure of the pneumatic pressure chamber 16 and the spring force of the coil spring 17, the internal volume of the liquid pressure regulating chamber 20 is enlarged and, at the same time, the valve 22 is closed. As a result, the excessive supply from the master cylinder 2 to the end brake 6 is cut off, the brake liquid pressure of the end brake 6 is reduced, and the locking of the brake is avoided. When the electromagnetic valve means 27 is turned OFF by the OFF-signal of the electronic control unit, the supply of liquid pressure from the pump 29 is cut off. When the liquid pressure of the liquid pressure chamber 25 is released to the liquid tank 31, the pressure differential responsive piston 8 and the liquid pressure regulating piston 7 are moved downward by the pressure of the pneumatic pressure chamber 16 and the spring force of the coil spring 17. The brake liquid pressure of the end brake 6 is increased by the compression of the liquid pressure regulating chamber 20.
However, the prior art as described above has problems. Corrosion on the inner wall surfaces of the large diameter cylinder 10 can build up over time. Scratches caused by upward and downward movement of the pressure differential responsive piston 8 also occur on the inner wall surfaces of the large diameter cylinder 10. In addition, dust or the like may enter between the seals 13, 14 and the inner wall sliding surface to impair sealing properties of the pneumatic pressure chamber 16. As a result, the pressure of the pneumatic chamber 16 is lost to vary the spring force, and when the air pressure sealed is set to a large value, the sliding resistance of the seal 14 increases to impair the quick-responsiveness of the pressure differential responsive piston 8. Moreover, when the mounting load of the coil spring 17 is increased, the apparatus become difficult to be miniaturized.